Conventionally known tube-stacking heat exchanger comprises a plurality of flat tubes being stacked one upon another, their ends are connected with a header tank, and a heat exchanger medium flows between an inlet joint and an outlet joint of the header tank in a serpentine form by making a plurality of turns.
The aforementioned flat tube for such tube-stacking heat exchanger is known, for example, as disclosed in (1) Japanese Utility Model Laid-Open Publication No. 59(1984)-59688 and (2) Japanese Patent Laid-Open Publication No. 3(1991)-155422.
The flat tube disclosed in the above-mentioned prior art (1) is, for example, as shown in FIG. 9, that a flat tube 2 comprises two plates 12 and 12 which are placed one upon the other, each plate having a plurality of projecting portions 16 projecting inwardly with their forward ends in pressure contact with projecting portions of the other plate, and connecting portions 14, 14 of edges of plates 12, 12 are joined together by brazing.
The flat tube disclosed in the above-mentioned prior art (2) is, for example, as shown in FIG. 10, that a flat tube 2 is formed by a single plate 12 of a predetermined size having a plurality of projecting portions (herein after called beads) 16, and the single plate 12 being folded into two at a center folding portion 13 and connecting portions 14, 14 of the edges are joined together by brazing.
For assembling and brazing the tube-stacking heat exchanger using the above-mentioned flat tubes, corrugated fins are placed alternately with a plurality of flat tubes, the ends of flat tubes are inserted into tube insertion holes of header tanks, and thus assembled body is placed on, for example, a belt conveyor, for fluxing the inside and then fluxing the outside, and finally the assembled body is brazed integrally in a furnace.
However, with conventional method of manufacturing the heat exchanger, the flux material does not reach the inner surface of each flat tube when fluxing after assembly of heat exchanger, because the flat tube was manufactured with the side edge connecting portions tightly connected with each other. This inconveniently causes defective brazing, namely, the inner surfaces of flat tubes are not properly brazed.
For this reason, conventional method includes two separate stages for fluxing inside and outside of each flat tube. For fluxing the inner surface of flat tube, a flux material is applied to the tube plate with a brush or roll.
However, for applying the fluxing material with brush it should be done manually which inevitably increases the number of manufacturing steps. Further, fluxing with a roll, the roll must be first immersed in the flux material and then the roll is pressed against the tube plate. In this manner, it is difficult to have the flux material properly deposited on the tube plate, and if the pressing of the roll against the tube plate is too strong, connecting portions of beads might be deformed.
The present invention provides a method of manufacturing tube-stacking heat exchanger assuring fluxing of the inner surface of each flat tube, regardless of whether the heat exchanger uses the flat tube formed by a single plate being folded into two or by two plates placed one upon the other.